PRKG1 and cardiac hypertrophy: PKG1 is a serine/threonine protein kinase that serves as an important mediator of the cGMP signaling pathway, is expressed in the cardiovascular system, and is a key mediator of the cellular effects of natriuretic peptides (NP) and nitric oxide (NO).32 Important biologic processes in which PKG is involved include tissue fibrosis, regulation of titin stiffness,33 and myocardial hypertrophy.